This invention relates to a non-invasive device and method for monitoring concentration levels of blood constituents in living subjects such as humans or animals, using a full spectrum of the near infrared portion of the light spectrum and adjacent visible spectrum in addition to discrete longer wavelengths of the near infrared region of the light spectrum.
1. Invasive Techniques
Invasive techniques of measuring blood constituents are in common usage. These techniques are painful, potentially dangerous and expensive to operate. A typical procedure is to obtain a blood sample from a vein and this sample is then tested in a medical laboratory, using a number of chemical procedures to measure each constituent separately. Alternatively, home glucose testing uses a finger puncture that is spotted onto an enzyme-based semi-permeable membrane test strip and is allowed to react for a certain length of time, with insulin administration then based upon either a visual colour comparison with a standard colour chart or by means of a more accurate and unambiguous spectroscopic technique (for example reflectance). There is a risk of infection and sometimes a patient can develop a rash when these invasive techniques are used.
2. Non-Invasive Techniques
Previous devices for non-invasively monitoring concentration of blood constituents of a patient are known. Usually, a sensor is used to externally measure either the concentration of the constituent in gases emitted by the body; the concentration contained in perspiration; or the concentration contained in body fluids such as tears, saliva or urine samples. An example of this approach is the GlucoWatch, developed by Cygnus. It draws interstitial fluid from a body part onto a patch and measures the glucose in that fluid. This approach is not ideal in that the patch causes irritation and each patch, which last for 12 hours, needs to be calibrated using a reference method which requires an invasive finger stick to obtain a blood sample. Alternatively, the blood constituent is measured using radiation passed through a part of the patient""s body such as the earlobe or reflected from a body part such as a finger or forearm. However, of the previous radiation devices, some have a radiation source which emits light in one wavelength only or two wavelengths (see for example U.S. Pat. No. 4,655,225; U.S. Pat. No. 4,883,953; and U.S. Pat. No. 4,882,492); other previous devices have more than one light source but have only a limited number of measuring wavelengths (U.S. Pat. Nos. 4,915,827; 5,028,787; 5,077,476; 5,237,178; 5,319,200 and 5,438,201)].
Some of these previous devices have had a number of discrete wavelength sources obtained through use of a broad-band lamp whose light is optically coupled through a number of light filters, each with its own designated transmission wavelength, to the test sample.
Further, some previous devices are controlled to take a series of measurements at successively higher or lower wavelengths. This can be extremely time consuming.
Other techniques have included those which measure a full spectrum of absorptions, with a large number (for example, 128 or 256) of wavelengths in a specific range and those that measure a limited number of wavelengths. Those that measure full spectra typically use the wavelengths in the 580 to 1100nm range (see for examples U.S. Pat. No. 5,361,758 and U.S. Pat. No. 4,975,581). An advantage of full spectra measurements is that they provide information about the desired analyte as well as information about interfering substances (e.g., other analytes) and effects (e.g., light scattering).
Some of the methods that measure a limited number of wavelengths utilize the 1100 to 1700 nm region because of sharper analyte spectra that exist in this region. Others measure at wavelengths in the 600 to 1100 nm region. These methods provide information relating to the analyte of interest, but fail to provide sufficient independent information about other analytes whose absorption interferes with the desired analyte.
Some previous devices which take measurements in earlobes do not take into account changes in the thickness of a patient""s earlobes compared to that of other patients or the change in size of a patient""s earlobes or the change in the transmission path length due to the pulsing of blood through the patient; or, they do not take into account temperature variations in the earlobes from patient to patient, or, the results fluctuate with prolonged operation.
Overall, previous non-invasive devices and techniques have not been sufficiently accurate to be used in place of invasive techniques in the measurement of blood constituent concentration levels by patients; or they have been designed to measure one component only and must be physically changed to measure for a different component; or, the devices take an unreasonably long time to produce a result; or, they cannot produce results in an easy-to-use form; or, they cannot measure the results of two or more constituents simultaneously. Obviously, if the device gives an inaccurate reading, disastrous results could occur for the patient using the device to calculate, for example, dosages for insulin administration.
The present invention provides a method for monitoring the concentration level of a particular constituent or, alternatively, of measuring the concentration level of more than one different constituents in a non-invasive device, the method producing result(s) in a short time period that is/are accurate and reliable.
The present inventors have determined that measurement at a continuum of wavelengths from 500 to 1100 nm provides information about the concentration of the desired analyte and very importantly further information about the many other analytes that interfere with an accurate measurement. The inventors have discovered that analyte measurement accuracy is enhanced by adding a limited number of discrete wavelength measurements in the 1100 to 1700 nm region to a full spectra absorption measurement of a continuum of wavelengths in the 500 to 1000 nm region. Using this combination it is possible to gain a significant improvement in analyte measurement accuracy. As used herein the 500-1100 nm region is referred to as the xe2x80x9cAV and NIR regionxe2x80x9d while the 1100-1700 nm region is referred to as the xe2x80x9clonger wavelength NIR regionxe2x80x9d or xe2x80x9cLWNIRxe2x80x9d.
According to preferred embodiments, in each case measurement of discrete wavelengths is at a sufficiently high signal to noise ratio in order to achieve desired results.
Accordingly, in its broad aspect, the present invention provides a method for monitoring the concentration level of a constituent in tissue comprising placing the tissue in a non-invasive device capable of emitting radiation; directing the radiation onto the tissue; measuring radiation collected from the tissue; calculating the concentration level based on the measured radiation wherein the radiation directed onto the tissue and collected from the tissue is of a continuum of wavelengths in the 500-1100 nm range, and discrete wavelengths in the range from 1100 to 1700 nm.
According to one aspect the present invention provides a method for measuring concentration levels of blood constituents within a living subject such as humans or animals wherein, in respect of the AV and NIR region, there is used a polychromatic light source or other radiation source that emits a broad spectrum of light in the range from 500 nm to 1100 nm. For this range, the method comprises the steps of directing light at a continuum of wavelengths simultaneously onto a bodypart of a subject; collecting the continuum of light after the light has been directed onto the part; focusing the collected light onto a grating, dispersing the continuum of light into a dispersed spectrum of component wavelengths of the collected light onto a linear array detector, the linear array detector taking measurements of at least one of transmitted and reflected light from the collected light in adjacent visible spectrum, and near infrared range from 500-1100 region, and the measurements are transferred to a microprocessor. With respect to the LWNIR region the method comprises the steps of directing one or more narrow band sources of light on the body part, collecting the one or more narrow bands on one or more detectors (depending on the specific configuration chosen), these measurements are also transferred to the microprocessor. The microprocessor then uses these measurements and a calibration algorithm to calculate the concentration level of said at least one constituent of said blood and tissue.
In another aspect of this invention, there is provided a method for determining a concentration of a constituent in a tissue of a subject comprising the steps of: irradiating the tissue with a broad spectrum of radiation in the AV and NIR region; irradiating the tissue with radiation in the longer wavelength NIR region; measuring at least one of transmitted or reflected radiation from the tissue at a continuum of wavelengths in the AV and NIR region and at one or more discrete wavelengths in the longer wavelength NIR region; and calculating the concentration of the constituent on the basis of the measurements, thereby determining the concentration of the constituent in the tissue.
Preferably, the continuum of wavelengths from the AV and NIR region is between 500 and 1100 nm
According to another embodiment, the discrete wavelength in the longer wavelength NIR region is between 1100 and 1700 nm.
According to yet another embodiment, one or more discrete wavelengths are between 1100 and 1300 nm.
According to another embodiment, one or more discrete wavelengths is between 1590 and 1700 nm.
According to another embodiment, at least two discrete wavelengths are measured at least one of which is between 1100 and 1300 nm and at least one of which is between 1590 and 1700 nm.
According to yet another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240 and 1250 nm.
According to another embodiment, the discrete wavelength measurements are at 1595, 1610 and 1620 nm.
According to another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240, and 1250 nm, and at 1595, 1610 and 1620 nm.
According to yet another embodiment, the radiation at each discrete wavelength is provided by a separate energy source.
According to another embodiment, the radiation at each of the discrete wavelengths is provided sequentially.
According to another embodiment the radiation at all of the discrete wavelengths is provided simultaneously.
According to another embodiment, a single energy source provides continuous energy over the radiation range of 1100 to 1300 nm.
According to another embodiment, there is provided a single energy source provides continuous energy over the radiation range of 1140 to 1260 nm.
According to another embodiment, a single energy source provides radiation in the range of 500 to 1300 nm.
According to another embodiment, the steps of irradiating the tissue in the AV and NIR region, and in the longer wavelength NIR region, are done simultaneously, and the measurement in each of said AV and NIR region and said longer wavelength NIR region is made simultaneously.
In yet other aspect of the present invention, there is provided a method for measuring concentration of a blood constituent within a body part of a living subject comprising:
irradiating a body part of the subject with a broad spectrum of radiation in the AV and NIR region;
collecting the radiation from the AV and NIR region after the radiation has been directed onto the part;
dispersing the collected radiation into a dispersed spectrum of component wavelengths onto a detector, the detector taking measurements of at least one of transmitted and reflected radiation from the collected radiation; transferring the measurements to a processor;
irradiating the body part of the subject with radiation in the longer wavelength NIR region;
detecting one or more discrete wavelengths in the longer wavelength NIR region after the radiation has been directed onto the part, the detector taking measurements of at least one of transmitted and reflected radiation; and
transferring the measurements to a processor; based on the measurements and one or more calibration algorithms, the processor calculating the concentration of said constituent of said blood.
According to one embodiment, the detector is a linear array detector and the measurement is of absorbed radiation.
According to another embodiment, the continuum of wavelengths from the AV and NIR region is between 500 and 1100 nm.
According to another embodiment, the discrete wavelength in the longer wavelength NIR region is between 1100 and 1700 nm.
According to another embodiment, the one or more discrete wavelengths are between 1100 and 1300 nm.
According to another embodiment, the one or more discrete wavelengths is between 1590 and 1700 nm.
According to another embodiment, at least two discrete wavelengths are measured at least one of which is between 1100 and 1300 nm and at least one of which is between 1590 and 1700 nm.
According to another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240 and 1250 nm.
According to another embodiment, the discrete wavelength measurements are at 1595, 1610 and 1620 nm.
According to another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240, and 1250 nm, and at 1595, 1610 and 1620 nm.
In yet another aspect of the present invention, there is provided a method for measuring concentration of a blood constituent within a body part of a living subject comprising:
irradiating the body part of the subject with a first continuum of a broad spectrum band of radiation in the AV and NIR region;
collecting the first band of radiation after the radiation has been directed onto the part;
dispersing the continuum of collected radiation into a dispersed spectrum of component wavelengths onto a detector, the detector taking measurements of at least one of transmitted and reflected radiation from the collected radiation; and
transferring the measurements to a processor;
irradiating the body part of the subject with a second continuum of a radiation band in the longer wave NIR region;
collecting the second band of radiation after the radiation has been directed onto the part;
dispersing the continuum of collected radiation into a dispersed spectrum of component wavelengths onto a detector;
detecting one or more discrete wavelengths in the longer wavelength NIR region;
the detector taking measurements of at least one of transmitted and reflected radiation from the collected radiation; and
transferring the measurements to a processor based on the measurements and one or more calibration algorithms, the processor calculating the concentration of said constituent of said blood, thereby determining.
According to one embodiment, the detector is a linear array detector and the measurement is of absorbed radiation.
According to another embodiment, the continuum of wavelengths from the AV and NIR region is between 500 and 1100 nm.
According to another embodiment, the discrete wavelength in the longer wavelength NIR region is between 1100 and 1700 nm.
According to another embodiment, the one or more discrete wavelengths are between 1100 and 1300 nm.
According to another embodiment, the one or more discrete wavelengths is between 1590 and 1700 nm.
According to another embodiment, at least two discrete wavelengths are measured at least one of which is between 1100 and 1300 nm and at least one of which is between 1590 and 1700 nm.
According to another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240 and 1250 nm.
According to another embodiment, the discrete wavelength measurements are at 1595, 1610 and 1620 nm.
According to another embodiment, the discrete wavelength measurements are at 1150, 1195, 1215, 1230, 1240, and 1250 nm, and at 1595, 1610 and 1620 nm.
According to another embodiment, the subject is a human and the body part is a finger.
According to another embodiment, the constituent is glucose, and the tissue is blood.
According to another embodiment a second source of radiation is provided for discrete wavelengths.